The mechanism of cardiac muscle contraction and relaxation depends on the flux of Ca2+ ions between the cytoplasm and sarcoplasmic reticulum (SR) within the myocytes. Phospholamban has a key role in Ca2+ transport by regulating the Ca2+ ATPase in SR membranes and by functioning as a Ca2+ selective channel. Phosphorylation of phospholamban is the event that determines to which cellular locality the Ca2+ ions will be directed and consequently the contractile state of the muscle tissue. The phospholamban channel is formed by five peptides and a structural model has been developed by researchers at Yale which predicts interhelical contacts consistent with mutagenesis results. The proposed work will test this model and provide atomic-level information on the effect of phosphorylation of the complex in a membrane environment. Specifically, MAS NMR and FTIR data will be collected on phosphorylated and nonphosphorylated samples labeled with 13C at unique positions. An understanding of the structure of the channel should provide insight into the mechanisms of ion flux and selectivity. Additionally, phospholamban may serve as a useful model for larger, more complex ion channels.